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  • Blackwell Science Ltd  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Na+ translocation by the NADH:ubiquinone oxidoreductase (complex I) from Klebsiella pneumoniae (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 33 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Complex I is the site for electrons entering the respiratory chain and therefore of prime importance for the conservation of cell energy. It is generally accepted that the complex I-catalysed oxidation of NADH by ubiquinone is coupled specifically to proton translocation across the membrane. In variance to this view, we show here that complex I of Klebsiella pneumoniae operates as a primary Na+ pump. Membranes from Klebsiella pneumoniae catalysed Na+-stimulated electron transfer from NADH or deaminoNADH to ubiquinone-1 (0.1–0.2 μmol min−1 mg−1). Upon NADH or deaminoNADH oxidation, Na+ ions were transported into the lumen of inverted membrane vesicles. Rate and extent of Na+ transport were significantly enhanced by the uncoupler carbonylcyanide-m-chlorophenylhydrazone (CCCP) to values of ≈0.2 μmol min−1 mg−1 protein. This characterizes the responsible enzyme as a primary Na+ pump. The uptake of sodium ions was severely inhibited by the complex I-specific inhibitor rotenone with deaminoNADH or NADH as substrate. N-terminal amino acid sequence analyses of the partially purified Na+-stimulated NADH:ubiquinone oxidoreductase from K. pneumoniae revealed that two polypeptides were highly similar to the NuoF and NuoG subunits from the H+-translocating NADH:ubiquinone oxidoreductases from enterobacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01506.x
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  • 2
    Electronic Resource
    Electronic Resource
    Enzymic and genetic basis for bacterial growth on malonate (1997)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 25 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Various bacteria are able to grow aerobically or anaerobically on malonate as sole source of carbon and energy. Independent of the mechanism for energy conservation, the decarboxylation of malonate is the key reaction in the decomposition of this compound. To achieve malonate decarboxylation under physiological conditions, the substrate must be converted into an activated (thioester) derivative. We report here on the malonate decarboxylases of Malonomonas rubra and Klebsiella pneumoniae. These enzymes perform an interesting substrate activation mechanism by generating a malonyl thioester with the enzyme. Formation of the malonyl-S-enzyme involves an ‘activation module’ that comprises the acetylation of a specific thiol group of an acyl carrier protein (ACP) and the transfer of the ACP moiety to malonate, yielding malonyl-S-ACP and acetate. The malonyl-S-ACP is subsequently decarboxylated with regeneration of the acetyl-ACP. The malonate activation mechanism is related to the activation of citrate by citrate lyase. The relationship extends to the identical 2′-(5′′-phosphoribosyl)-3′-dephospho-CoA thiol cofactor that is bound covalently to the corresponding ACP subunit. In Klebsiella pneumoniae, malonate is decarboxylated by a water-soluble enzyme complex. In the anaerobic bacterium Malonomonas rubra, malonate decarboxylation is catalysed by a set of water-soluble as well as membrane-bound enzymes that function together in converting the free energy of the decarboxylation reaction into ΔμNa+. Therefore, this malonate decarboxylase includes a biotin carrier protein that accepts the CO2 moiety from malonyl-S-ACP and delivers it to a membrane-bound decarboxylase acting as a Na+ pump. Genes encoding the individual protein components that perform the decarboxylation of malonate in K. pneumoniae or M. rubra have been identified within the mdc and mad gene clusters respectively. The function of most of the derived proteins could be envisaged from sequence similarities with proteins of known functions. The genetic evidence firmly supports the idea that malonate decarboxylation is carried out by the two different decarboxylases, as deduced from the biochemical studies of the enzymes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.4611824.x
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  • 3
    Electronic Resource
    Electronic Resource
    Na+ translocation by complex I (NADH:quinone oxidoreductase) of Escherichia coli (2000)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 35 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Following on from our previous discovery of Na+ pumping by the NADH:ubiquinone oxidoreductase (complex I) of Klebsiella pneumoniae, we show here that complex I from Escherichia coli is a Na+ pump as well. Our study object was the Escherichia coli mutant EP432, which lacks the Na+/H+ antiporter genes nhaA and nhaB and is therefore unable to grow on LB medium at elevated Na+ concentrations. During growth on mineral medium, the Na+ tolerance of E. coli EP432 was influenced by the organic substrate. NaCl up to 450 mM did not affect growth on glycerol and fumarate, but growth on glucose was inhibited. Correlated to the Na+ tolerance was an increased synthesis of complex I in the glycerol/fumarate medium. Inverted membrane vesicles catalysed respiratory Na+ uptake with NADH as electron donor. The sodium ion transport activity of vesicles from glycerol/fumarate-grown cells was 40 nmol mg−1 min−1 and was resistant to the uncoupler carbonyl-cyanide m-chlorophenylhydrazone (CCCP), but was inhibited by the complex I-specific inhibitor rotenone. With an E. coli mutant deficient in complex I, the Na+ transport activity was low (1–3 nmol mg−1 min−1), and rotenone was without effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01712.x
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  • 4
    Electronic Resource
    Electronic Resource
    Regulation of anaerobic citrate metabolism in Klebsiella pneumoniae (1995)
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Science Ltd
    Molecular microbiology 18 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Three enzymes are specifically required for uptake and catabolism of citrate by Klebsiella pneumoniae under anaerobic conditions: a Na+-dependent citrate carrier (CitS), citrate lyase (CitDEF), and the Na+ pump oxalo-acetate decarboxylase (OadGAB). The corresponding genes are clustered on the chromosome, with the citCDEFG genes located upstream and divergent to the citS—oadGAB genes. We found that expression of citS from its native promoter in Escherichia coli requires the DNA region downstream of oadB. Nucleotide sequence analysis of this region revealed the presence of two adjacent genes, citA and citB, By sequence similarity, the predicted CitA and CitB proteins were identified as members of the two-component regulatory systems. The sensor kinase CitA contained, in the N-terminal half, two putative transmembrane helices which enclosed a presumably periplasmic domain of about 130 amino acids. The C-terminal half of the response regulator CitB harboured a helix-turn-helix motif typical of DNA-binding proteins. K. pneumoniaecitB null mutants were unable to grow anaerobically with citrate as the sole carbon and energy source (Cit− phenotype). When cultivated anaerobically with citrate plus glycerol, all of the citrate-specific fermentation enzymes were synthesized in the wild type, but not in the citB mutants. This showed that citS, oadGAB and citDEF required the CitB protein for expression and therefore are part of a regulon. In the wild type, synthesis of CitS, oxalo-acetate decarboxylase and citrate lyase was dependent on the presence of citrate, sodium ions and a low oxygen tension. In a citA null mutant which expressed citB constitutively at high levels, none of these signals was required for the formation of the citrate fermentation enzymes. This result suggested that citrate, Na+, and oxygen exerted their regulatory effects via the CitA/CitB system. In the presence of these signals, the citAB gene products induced their own synthesis. The positive autoregulation occurred via co-transcription of citAB with citS and oadGAB.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.mmi_18030533.x
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